ip6.mx.mostelekom.net has no MX records.
Question and response
Question
dig ip6.mx.mostelekom.net. MX
Answer
The response has no answer records.
Authority
mostelekom.net. 86400 SOA ns1.ncnet.ru. noc.ncnet.ru. 2019081901 10800 900 604800 86400
Additional
. 0 OPT ; payload 1460, xrcode 0, version 0, flags 0